1. Field of the Invention
This invention relates to a light receiving device for a photoelectric element in an exposure meter. More particularly, the invention is concerned with an improved construction of the light receiving element for the purpose of enabling it to receive the maximum possible amount of light.
2. Description of the Prior Art
The technique of collecting light on a light receiving surface of a photoelectric element from a wide angle by adhering a substantially semi-circular lens to the light receiving surface has long been known. However, in utilizing this technique for increasing illumination on the light receiving surface of the photoelectric element, such as a silicon photo diode, in an exposure meter which is built into a photographic camera, there inevitably arise various problems such as those to be exemplified below.
Firstly, a technique of forming a substantially semi-circular light-converging lens by natural dripping of a liquid transparent resin such as epoxy resin, etc. on a chip of a photoelectric element has already been utilized in light emitting diodes. However, in this dripping technique, precision in the lens-shaped swelling is difficult to control with the result that considerable fluctuations occur in the light converging characteristic of each lens-shaped swelling, so that it is not always suitable for the exposure meter.
Secondly, a thin glass filter is adhered to the surface of the silicon photo diode for the exposure meter, the purpose of which is to correct a visual sensitivity, i.e. to permit light of a wavelength to be measured to pass therethrough. Further adherence onto this glass surface of acrylic resin in the form of a semi-circular lens apprehensively causes exfoliation or breakage of the filter glass due to thermal shock imparted thereto, such as by abrupt change in the temperature, which thermal shock is brought about by the difference in the thermal expansion coefficient between acrylic resin and glass. Nevertheless, when this semi-circular lens is made of glass, the difficulty in adhering the same onto the glass filters may be lessened, but the cost of polishing the semi-circular lens made of glass having a diameter of as small as a few millimeter is exceedingly high with the consequence that the light receiving device thus obtained becomes disadvantageously expensive.
Thirdly, regardless of whether the filter if made of glass or not, or whatever method may be adopted, the assembly cost necessary for controlling precision of the adhering position of the lens with respect to the chip is significant.
Fourthly, in case the lens and the photoelectric element are to be adhered together, if they are adhered with the optical axis of the lens being deviated from the center of the chip, the resultant element cannot be repaired and its rate of yield becomes remarkably inferior.